U.S. patent application number 11/910418 was filed with the patent office on 2009-06-04 for shock absorber for movable tools.
This patent application is currently assigned to MORPHIC TECHNOLOGIES AKTIEBOLAG (publ). Invention is credited to Bjorn Arvidsson, Anders Dahlberg, Hakan Olsson.
Application Number | 20090139812 11/910418 |
Document ID | / |
Family ID | 37053626 |
Filed Date | 2009-06-04 |
United States Patent
Application |
20090139812 |
Kind Code |
A1 |
Olsson; Hakan ; et
al. |
June 4, 2009 |
SHOCK ABSORBER FOR MOVABLE TOOLS
Abstract
The invention relates to a shock absorber in which the blow from
a movable tool is received by a piston that transmits the kinetic
energy of the blow to a chamber filled with hydraulic liquid. The
shock absorber is also provided with means for returning the piston
to its starting position, after the blow has been absorbed. The
means of the shock absorber, for returning the piston, can be
hydraulic means acting on the piston.
Inventors: |
Olsson; Hakan; (Karlskoga,
SE) ; Dahlberg; Anders; (Lerum, SE) ;
Arvidsson; Bjorn; (Stenhamra, SE) |
Correspondence
Address: |
PILLSBURY WINTHROP SHAW PITTMAN, LLP
P.O. BOX 10500
MCLEAN
VA
22102
US
|
Assignee: |
MORPHIC TECHNOLOGIES AKTIEBOLAG
(publ)
Karlskoga
SE
|
Family ID: |
37053626 |
Appl. No.: |
11/910418 |
Filed: |
April 1, 2005 |
PCT Filed: |
April 1, 2005 |
PCT NO: |
PCT/SE05/00473 |
371 Date: |
October 1, 2007 |
Current U.S.
Class: |
188/269 |
Current CPC
Class: |
B21D 24/02 20130101;
F16F 9/18 20130101 |
Class at
Publication: |
188/269 |
International
Class: |
F16F 9/06 20060101
F16F009/06 |
Claims
1) A shock absorber (1) for machines having a movable tool (2),
which shock absorber (1) comprises: a) a housing (3) with a first
chamber (4) filled with a pressurized hydraulic liquid, and b) at
least one first piston (7) that is movably arranged inside the
housing (3) and is arranged in a first end (8) thereof to be able
to receive a blow from a movable tool (2) and by its motion to
transmit kinetic energy from the blow to the hydraulic liquid in
the first chamber (4), and c) means (4b, 22, 24, 38, 39, 41) for
returning the first piston (7) to its starting position, after the
blow, such that the piston (7) is able to receive a new blow.
2) A shock absorber according to claim 1, characterised in that
said means for returning the first piston (7) comprises a chamber
(4, 5) with a pressurized hydraulic liquid that acts on a surface
area (24, 41) of the first piston (7) in such a direction that the
piston (7) is pressed in a direction towards its starting
position.
3) A shock absorber according to claim 2, characterised in that the
piston (7) is arranged with its ends positioned in different
chambers (5, 20), the surface areas (24, 22) of the piston's (7)
ends and the pressure in the two chambers (5, 20) being chosen such
that a resulting force acts to return the piston (7) to its
starting position.
4) A shock absorber (1) according to claim 3, characterised in that
the two chambers (5, 20) are connected to a source (12) of
pressurised hydraulic liquid, which is in common for the two
chambers (5, 20), and that a distal end of the piston (7), as seen
in the direction of the blow, has a larger surface area (24), while
a proximal end of the piston (7), as seen in the direction of the
blow, has a smaller surface area (22), such that the resulting
compressive force from the hydraulic liquid strives to return the
piston (7).
5) A shock absorber according to claim 2, characterised in that the
first chamber (4) is divided into a subchamber (4b) that is distal
in relation to the first end of the piston, and a subchamber (4a)
that is proximal in relation to the first end of the piston (7),
and in that said means for returning the first piston (7) to its
starting position after the blow comprises a collar (39) on the
first piston (7), which collar has a distal surface area (41) and a
proximal surface area (42), which proximal surface area (42) is
smaller than the distal surface area (41).
6) A shock absorber (1) according to claim 1, characterised in that
the housing (3) of the shock absorber is provided with a second
chamber (5) filled with a pressurized hydraulic liquid, which
second chamber (5) is connected to the first chamber (4) via a
first non return valve (6) arranged to open when the pressure in
the second chamber (5) is greater than the pressure in the first
chamber (4), that the second end (9) of the first piston is
positioned in the second chamber (5), such that a blow from a
movable tool (2) can make said first piston (7) move inwards into
the second chamber (5), thereby to increase the pressure in the
second chamber (5) to a level at which the first non return valve
(6) opens, such that pressurized hydraulic liquid starts to flow
from the second chamber (5) to the first chamber (4), and the first
chamber (4) having an outlet (10) arranged to allow for inflow and
outflow of hydraulic liquid, to and from, respectively, the first
chamber (4).
7) A shock absorber (1) according to claim 6, characterised in that
the second chamber (5) is connected, via a second non return valve
(11), to a source (12) of a pressurized hydraulic liquid, such that
the second non return valve (11) opens when the pressure in the
second chamber (5) is below a predetermined level.
8) A shock absorber (1) according to claim 7, characterised in that
the housing (3) is provided with a third chamber (13), and that the
first piston (7) is provided with at least one stop (14) arranged
to meet a limiting surface area (15) of the third chamber (13),
such that the piston's (7) movement is limited in a direction
opposite the direction of the blow, such that the first piston (7)
reaches a proximal end position, as seen in relation to the movable
tool (2), when the stop (14) of the first piston (7) meets said
limiting surface area (15).
9) A shock absorber according to claim 8, characterised in that the
third chamber (13) is a gas filled chamber (13) in which the
pressure preferably is the same as the atmospheric pressure.
10) A shock absorber (1) according to claim 9, characterised in
that the shock absorber (1) comprises a second piston (17) arranged
to be movable inside the housing (3), and arranged at a first end
(18) thereof to get in direct contact with the movable tool (2),
and at a second end (19) thereof to face the first end (8) of the
first piston (7), such that a blow from the movable tool (2) can be
transmitted to the first piston (7) via the second piston (17).
11) A shock absorber (1) according to claim 8, characterised in
that the housing (3) is provided with a fourth chamber (20) into
which the first end (8) of the first piston (7) extends when the
first piston (7) reaches its end position which is proximal in
relation to the movable tool (2).
12) A shock absorber (1) according to claim 11, characterised in
that the fourth chamber (20) is filled with a pressurized hydraulic
liquid, and that, in a starting position for the shock absorber
(1), a gap (D) is arranged between the first end (8) of the first
piston (7) and the second end (19) of the second piston (17), such
that the second piston (17) must move a certain distance (D) before
it is able to transmit a blow from the movable tool (2) to the
first piston (7).
13) A shock absorber (1) according to claim 12, characterised in
that the second end (19) of the second piston (17) and the first
end (8) of the first piston have planar surface areas (22, 23) that
are parallel to each other and which end surface areas (22, 23) are
preferably of equal size.
14) A shock absorber (1) according to claim 13, characterised in
that the fourth chamber (20) is connected, via a third non return
valve (25), to a source (12) of a pressurized hydraulic liquid,
such that the third non return valve (25) opens when the pressure
in the fourth chamber (20) is below a predetermined level.
15) A shock absorber according to claim 14, characterised in that
the second chamber (5) and the fourth chamber (20) are connected to
the same source (12) of pressurized hydraulic liquid.
16) A shock absorber (1) according to claim 7, characterised in
that the outlet (10) of the first chamber (4) is connected to an
accumulator (26) for hydraulic liquid.
17) A shock absorber (1) according to claim 12, characterised in
that the fourth chamber (20) has an outlet (27) arranged to let out
hydraulic liquid when the pressure in the fourth chamber (20)
exceeds a predetermined level.
18) A shock absorber (1) according to claim 17, characterised in
that the outlet (27) of the fourth chamber (20) is connected to an
accumulator (28) for hydraulic liquid.
19) A shock absorber according to claim 7, characterised in that
the first non return valve (6) is loaded by at least one elastic
element (29) that presses the first non return valve (6) towards a
closed position.
Description
TECHNICAL FIELD
[0001] The present invention relates to a shock absorber for a
movable tool, primarily a hydraulic shock absorber, and it is
intended to be used particularly as a shock absorber in machines
operating in a cycle and having a movable tool. The shock absorber
according to the invention is intended primarily to be used in
machines for cutting and punching of metals and other materials in
the form of wires, bars, profiles, strips and the like.
BACKGROUND OF THE INVENTION
[0002] Machines that make use of kinetic energy for various working
operations such as cutting and punching have existed for long and
in many different forms. Many of them have in common that a movable
mass, such as a ram, is accelerated rectilinearly in order to hit a
movable tool, such as a punching or cutting tool that cooperates
with a fixed tool to perform the actual working operation, such as
a cutting operation. The movable tool has a certain remaining
velocity and thereby a certain remaining kinetic energy after the
working operation, i.e. a residual energy. This residual energy
must be absorbed by a shock absorber. Such a shock absorber is
often positioned on the side opposite to the movable tool, as seen
from the ram. Various types of shock absorbers are known from e.g.
U.S. Pat. No. 4,339,975, U.S. Pat. No. 4,311,086 and U.S. Pat. No.
5,673,601.
[0003] When the working operation is finished and the movable tool
has been braked in a manner that is suitable for the process and as
gentle as possible for the machinery, the movable tool must be
returned to its initial position in order to be able to perform a
new working blow. When this has taken place, new material can be
fed forward for the next working operation.
[0004] Accordingly, two functions have to be handled in connection
with machines with movable tools. Firstly, one must be able to
brake the motion of the movable tool after the working operation
(such as a cutting operation). Secondly, one must be able to return
the movable tool before the next working operation. The switching
between these two functions can be maneuvered actively from the
machine's control system, or passively, without interference from
external units. The active variant requires accurate
synchronisation and knowledge of the size of the residual energy in
order to ensure that all kinetic energy is really absorbed before a
switch in function. A passive shock absorber handles this in
itself, and switches functions when shock absorbing is completed
and it is time to return the tool.
[0005] It is desirable for a shock absorber for kinetic machines to
absorb as much as possible of the supplied residual energy and to
return as little as possible. Designs that use elastomers or air
all have the characteristic that a large portion of the residual
energy is returned to the movable tool, whereby the tool bounces
against the shock absorber instead of being slowed down and
stopped. Several known hydraulic shock absorbers also have this
drawback, partly due to the compressibility of the hydraulic
liquid, the effect of which is easily underestimated.
[0006] A desirable property of a shock absorber for kinetic cutting
machines is that the shock absorber slows down the tool's movement
as little as possible during initial tool movement, when the actual
cutting operation takes place. It is optimal if the tool is not
slowed down at all, for example by the part of the shock absorber
that is applied against the tool in order to slow down its movement
is not at all in contact with the tool when the ram hits the tool,
but is applied only after a short distance of movement. Such a
device is very hard to realize without having to make the shock
absorber active. This is because the returning of the tool requires
some device to in reality bring the movable tool to its return
position. A shock absorber without a forced returning power is
difficult to make as fast and reliable as is a shock absorber that
utilises a forced returning power. Accordingly, the movable tool is
often returned by a device that presses the movable tool against a
stop and thereby aligns the fixed and the movable tools. For the
optimal case to result, this device must be withdrawn after the
material has been brought through the tools, but before the ram
hits the tool, a time period of about 10 to 100 milliseconds,
depending on the size of the machine. This is far from impossible,
but a malfunctioning of such a device may result in breakdown,
operations disturbance or the production of faulty components.
[0007] It is an object of the present invention to provide an
improved shock absorber for machines having a movable tool, being
able to slow down the movement fast, to absorb the kinetic energy
and to return the movable tool to its starting point. Furthermore,
it is an objective of the invention for the shock absorber to slow
down the movement of the movable tool as little as possible in the
beginning of a working operation. These and other objective can be
realised by the present invention, which is clear from the
following description.
ACCOUNT OF THE INVENTION
[0008] The invention relates to a hydraulic shock absorber for
machines operating in a cycle and having a movable tool. The shock
absorber comprises a housing with a first chamber that is filled
with a hydraulic liquid, and at least a first piston that is
movably arranged in the housing. The piston is arranged in a first
end thereof to receive a blow from a movable tool, and by its
motion to transmit kinetic energy from the blow to the hydraulic
liquid in the first chamber. The shock absorber also comprises
means for returning the first piston to its starting position,
after the blow, such that the piston can receive a new blow. Said
means for returning the first piston may comprise a chamber with a
pressurized hydraulic liquid that acts on a surface area of the
first piston in such a direction that the piston is pressed in a
direction towards its starting position.
[0009] In one embodiment of the invention, the piston is arranged
to have its ends positioned in different chambers, the areas of the
ends of the pistons and the pressure in the two chambers being
chosen such that a compressive force from the hydraulic liquid acts
to return the piston to its starting position. Both chambers can
then be connected to a source of a pressurized hydraulic liquid,
which source is in common for the two chambers. A distal end of the
piston, as seen in the direction of the blow, will then have a
larger surface area, while a proximal end of the piston, as seen in
the direction of the blow, will have a smaller surface area, such
that the resulting compressive force from the hydraulic liquid
strives to return the piston to its starting position.
[0010] According to another embodiment, said first chamber can be
divided in a sub-chamber that is distal in relation to the first
end of the piston, and a subchamber that is proximal in relation to
the first end of the piston. Said means for returning the first
piston to its starting position after the blow may then comprise a
collar on the first piston, which collar has a distal surface area
and a proximal surface area, which proximal surface area is smaller
than the distal surface area.
[0011] In a preferred embodiment, the shock absorber according to
the invention comprises a housing having a first chamber filled
with a pressurized hydraulic liquid, and a second housing filled
with a pressurized hydraulic liquid. The second chamber is
connected with the first chamber via a first non return valve that
is arranged to open when the pressure in the second chamber is
greater than the pressure in the first chamber. The shock absorber
further comprises at least a first piston that is arranged to be
movable in the housing, and that is arranged in a first end thereof
to be able to receive a blow from a movable tool. A second end of
said first piston is positioned in the second chamber, whereby a
blow from a movable tool can make said first piston move inwards in
the second chamber, thereby to increase the pressure in the second
chamber to a level at which the first non return valve opens When
the first non return valve opens, pressurized hydraulic liquid will
start to flow from the second chamber to the first chamber. The
first chamber has furthermore (in preferred embodiments) an outlet
adapted to allow for inflow and outflow of hydraulic liquid to or
from, respectively, the first chamber. In preferred embodiments,
the first non return valve may be loaded by one or more elastic
elements pressing the first non return valve towards a closed
position.
[0012] In advantageous embodiments, the second chamber is
connected, via a second non return valve, to a source of a
pressurized hydraulic liquid, such that the second non return valve
opens when the pressure in the second chamber decreases a
pre-determined level. Embodiments are however conceivable in which
the second non return valve and its connection to a source of
pressurized hydraulic liquid is not used.
[0013] In preferred embodiments, the housing is provided with a
third chamber and in that case the first piston is provided with at
least one stop arranged to meet a limiting surface area of the
third chamber. Thereby, the piston's movement is limited in a
direction opposite the direction of the blow, such that the first
piston will reach a proximal end position, as seen in relation to
the movable tool, when the stop of the first piston meets said
limiting surface area.
[0014] In preferred embodiments, the third chamber is a gas filled
chamber in which the pressure preferably is the same as the
atmospheric pressure.
[0015] The invention is primarily intended to be a passive shock
absorber. In preferred embodiments of the invention, the shock
absorber comprises a second piston--a shock absorbing piston--that
preferably bears continuously against the movable tool. The second
piston is arranged to be movable inside the housing, and is
arranged at a first end thereof to get in direct contact with the
movable tool, and at a second end thereof to face the first end of
the first piston, such that a blow of the movable tool can be
transmitted to the first piston via the second piston. Preferably,
the second piston or the shock absorbing piston has a minimal
weight and diameter (it should be realised however that the weight
and diameter is influenced by several factors, such as a required
strength). Suitably, it may bear against the movable tool by a
fairly moderate force, enough only to secure that the tool is
returned within a short enough time period. How long this time
period is, how long time that the tool blocks the feeding forward
of new material, may depend on several factors, such as a desired
maximum production rate.
[0016] The housing is suitably provided with a fourth chamber into
which the first end of the first piston extends when the first
piston reaches its end position which is proximal in relation to
the movable tool. In a preferred embodiment, the fourth chamber is
filled with a pressurized hydraulic liquid. A gap may exist between
the first end of the first piston and the second end of the second
piston, when the shock absorber is in a starting position. Then,
the second piston must move a certain distance before it can
transmit a blow from the movable tool to the first piston.
[0017] The second end of the second piston and the first end of the
first piston preferably have planar surface areas that are parallel
to each other. In this case, the end surface areas are preferably
equal in size.
[0018] The fourth chamber can be connected via a third non return
valve to a source of a pressurized hydraulic liquid, such that the
third non return valve opens when the pressure in the fourth
chamber decreases a predetermined level. In this case, the second
chamber and the fourth chamber are suitably connected to the same
source of pressurized hydraulic liquid.
[0019] In a particularly advantageous embodiment of the invention,
the outlet of the first chamber is connected to an accumulator for
hydraulic liquid. The accumulator can be used among other things to
contribute to the driving of the movable tool.
[0020] Suitably, the fourth chamber has an outlet arranged to allow
for inflow and outflow of hydraulic liquid, to and from,
respectively, the fourth chamber. In advantageous embodiments of
the invention, the outlet of the fourth chamber is also connected
to an accumulator for hydraulic liquid.
[0021] In its second end, the first piston has an end surface area
that in advantageous embodiments is larger than the end surface
area of the first end.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] FIG. 1 is a schematic representation of a kinetic cutting
machine using a shock absorber that can be a shock absorber
according to the present invention.
[0023] FIG. 2 shows the same cutting machine as in FIG. 1, but here
immediately after the machine has made an operating stroke.
[0024] FIG. 3 shows, in a cross-section according to A-A in FIG. 1,
the shock absorber according to the invention in a first position
before the movable tool has made its stroke. Here, the shock
absorber is in a resting position.
[0025] FIG. 4 is a magnification of some details in FIG. 3.
[0026] FIG. 5 shows a view corresponding to FIG. 3, but in which
the movable tool has made a stroke and the shock absorber according
to the invention has started to receive the blow from the movable
tool.
[0027] FIG. 6 shows a view corresponding to FIG. 3 and FIG. 5, in
which the first piston has begun to be pressed into the second
chamber, by the blow of the movable tool.
[0028] FIG. 7 shows a view corresponding to FIG. 6, in which the
first non return valve has been opened and hydraulic liquid flows
from the second chamber and into the first chamber.
[0029] FIG. 8 shows a position in which the first non return valve
is starting to close.
[0030] FIG. 9 shows a position in which the first non return valve
has returned to a closed position, but in which the first piston
has not yet returned to its starting position.
[0031] FIG. 10 shows a position in which the pistons are about to
be returned.
[0032] FIG. 11 shows a position in which the movable tool is about
to be aligned in the proper position.
[0033] FIG. 12 shows the shock absorber and the movable tool once
again in a starting position for a new operating stroke.
[0034] FIG. 13 shows in perspective a conceivable design of the
first non return valve.
[0035] FIG. 14 shows an embodiment of the invention in which it is
possible to vary the distance that the second piston moves before
it gets in contact with the first piston.
[0036] FIG. 15 shows a part of the embodiment shown in FIG. 14, in
greater detail.
[0037] FIG. 16 shows yet an embodiment of the invention, in which
the first chamber of the shock absorber has been given a different
design.
[0038] FIG. 17 is a magnification of a part of FIG. 16.
DETAILED DESCRIPTION OF THE INVENTION
[0039] In the following, the invention will be explained while
referring to a case in which the invention is used in connection
with a kinetic cutting machine for wires and bars. It should be
understood however that the shock absorber according to the
invention can be used also for other machines operating in a cycle
and having a movable tool. FIG. 1 shows a work piece W in the form
of a wire or a bar W that has been fed forward to a machine with a
fixed tool F and a movable tool 2. The movable tool 2 has a through
hole 31 for the wire or the bar W, and there is also a
corresponding through hole in the fixed tool F. Then, the work
piece W can be brought to pass through the fixed tool F and into
the movable tool 2. In connection with the movable tool 2, there is
a piston P that is able to make an operating stroke against the
movable tool 2. FIG. 2 shows how the piston P has made a blow
against the movable tool 2, such that the movable tool 2 is no
longer in its original position. The fixed tool F is however still
in its original position. The through holes in the fixed F tool and
the movable tool 2 will then no longer be aligned. The part of the
work piece W that is inside the movable tool 2 has then been blown
off from the rest of the work piece W. As is shown in FIG. 2, the
movable tool 2 will hit the shock absorber 1. The shock absorber 1
should then be able to brake the movement of the movable tool 2,
and most preferably also be able to return the movable tool 2 to
its starting position. As soon as the movable tool 2 has been
returned to its starting position, such that the through holes of
the tools are aligned, the work piece W can be fed forward. Unless
already removed, the previously cut part of the work piece, left in
the movable tool, will be pushed out when the work piece W is fed
forward.
[0040] An advantageous embodiment of the invention will now be
described in greater detail with reference to FIGS. 3 and 4. FIG. 3
shows a hydraulic shock absorber 1 for machines operating in a
cycle. FIG. 3 shows, at the bottom end thereof, a movable tool 2,
the movement of which the shock absorber according to the invention
is intended to brake. The shock absorber 1 comprises a housing 3
having a first chamber 4. The first chamber 4 is filled with a
pressurized hydraulic liquid. The housing 3 also has a second
chamber 5, which is also filled with a pressurized hydraulic
liquid. The second chamber 5 is connected with the first chamber 4
via a first non return valve 6 that is arranged to open when the
pressure in the second chamber 5 is greater than the pressure in
the first chamber 4. The drawings show how one or more
conduits/channels 35 connect the first chamber 4 with the second
chamber 5, and how the first non return valve 6 is positioned in
connection with an outlet for the channel or channels 35, which
outlet leads into the first chamber 4 when the first non return
valve 6 is open. The shock absorber further comprises at least a
first piston 7 that is arranged to be movable in the housing 3. The
first piston 7 is arranged in a first end 8 thereof to be able to
receive a blow from a movable tool 2. A second end 9 of the first
piston 7 is positioned in the second chamber 5. A blow from a
movable tool 2 will then make said first piston 7 move inwards in
the second chamber 5. Thereby, the pressure in the second chamber 5
will be raised to a level at which the first non return valve 6
opens, and pressurized hydraulic liquid starts to flow from the
second chamber 5 into the first chamber 4. The first chamber 4 has
furthermore an outlet 10 arranged to allow for inflow and outflow
of hydraulic liquid, to and from, respectively, the first chamber
4. In advantageous embodiments of the invention, the second chamber
5 is connected, via a second non return valve 11, to a source 12 of
a pressurized hydraulic liquid, such that the second non return
valve 11 opens when the pressure in the second chamber 5 decreases
a predetermined level.
[0041] In preferred embodiments, the housing 3 is provided with a
third chamber 13. Then, the first piston 7 may be provided with at
least one stop 14 arranged to meet a limiting surface area 15 of
the third chamber 13. Then, the movement 7 of the piston can be
limited in a direction opposite the direction of the blow. The
first piston 7 will accordingly reach an end position that is
proximal in relation to the movable tool 2, when the stop 14 of the
first piston 7 meets said limiting surface area 15. In a preferred
embodiment, said stop 14 may be a lower surface area 14 on an upper
part of the first piston 7, which upper part of the piston has a
larger diameter. In practice, it can be suitable to use pistons
having a circular cylindrical shape, even if other shapes are
conceivable as such. Then, the stop 14 can be achieved by the
piston 7 having a diameter transition from a smaller diameter to a
larger diameter. It should be realised however that the stop could
be otherwise formed. The limiting surface area 15 of the third
chamber 13 is here shown as the upper surface area of a ring 30
that is positioned on the bottom of the third chamber 13. The ring
30 can be made of an elastomer, such as rubber. This will result in
a gentler braking of the first piston 7, during the return.
[0042] In preferred embodiments of the invention, the third chamber
13 is a gas filled chamber 13 in which the pressure preferably is
the same as the atmospheric pressure.
[0043] The shock absorber 1 could advantageously comprise a second
piston 17 arranged in the housing 3. The second piston 17 is then
arranged at a first end 18 thereof to get in direct contact with
the movable tool 2, and at a second end 19 thereof to face the
first end 8 of the first piston 7. Thereby, a blow of the movable
tool 2 can be transmitted to the first piston 7 via the second
piston 17. Advantageously, the second piston 17 could have a flange
that prevents the piston 17 from being pushed out from the shock
absorber 1 if the shock absorber is pressurized by mistake without
the piston 17 bearing against a tool 2.
[0044] The housing 3 may further have a fourth chamber 20 into
which the first end 8 of the first piston 7 extends when the first
piston 7 reaches its end position which is proximal in relation to
the movable tool 2. Then, the fourth chamber 20 is filled with a
pressurized hydraulic liquid. As is best seen in FIG. 4, a gap D is
arranged between the first end 8 of the first piston 7 and the
second end 19 of the second piston 17, in a starting position for
the shock absorber 1. Then, the second piston 17 must move a
certain distance D before it can transmit a blow from the movable
tool 2 to the first piston 7. The second end 19 of the second
piston 17 and the first end 8 of the first piston preferably have
planar surface areas 22, 23, that are parallel to each other. The
end surface areas 22, 23 are preferably equal in size. FIG. 3 for
example shows how the fourth chamber 20 can be connected to a
source 12 of pressurized hydraulic liquid. The connection may
comprise a third non return valve 25, and may be designed such that
the third non return valve 25 opens when the pressure in the fourth
chamber 20 decreases a predetermined level. In preferred
embodiments, the second chamber 5 and the fourth chamber 20 are
suitably connected to the same source 12 of pressurized hydraulic
liquid. In the drawings, the upper surface area 23 of the second
piston 17 is shown to be of equal size as the lower surface area 22
of the first piston 7. It is however conceivable that the lower
surface area 22 of the first piston 7 is of equal size as the
cross-sectional area of the piston rod of the second piston 17. In
that case, the advantage is achieved that no oil is transported
into or out from the fourth chamber 20 when the two pistons 7, 17
move concurrently.
[0045] In a particularly advantageous embodiment, the outlet 10 of
the first chamber 4 is connected to an accumulator 26 for hydraulic
liquid. An accumulator that is suitable for this purpose is sold
by, among others, HYDAC INTERNATIONAL GmbH having the address
Postfach 1251 Sulzbach/Saar, Germany. HYDAC sells a type of
accumulator that is called bladder accumulator (German:
"Blasenspeicher"). A particularly suitable type of accumulator is
the type of accumulator that by HYDAC is called a "High-Flow
bladder accumulator" (German: "High-Flow Blasenspeicher"). In
Sweden, such accumulators can be purchased from HYDAC Fluidteknik
AB having the address Karlsbodavagen 39, Mariehall, Box 20112,
S-16102 BROMMA. It should be understood however that HYDAC is but
one supplier of many, and that suitable bladder accumulators can be
obtained also from other suppliers. The accumulator 26 that is
arranged to receive hydraulic liquid from the first chamber 4, can
be used to drive the piston P that is used to give the movable tool
2 a blow.
[0046] In embodiments having a fourth chamber, the fourth chamber
20 too can have an outlet 27 that is arranged to allow for inflow
and outflow of hydraulic liquid, to or from, respectively, the
fourth chamber 20. The outlet 27 of the fourth chamber 20 may then
be connected to an accumulator 28 for hydraulic liquid. This
accumulator too can e.g. be a High-Flow bladder accumulator from
HYDAC.
[0047] In preferred embodiments of the invention, the first non
return valve 6 may be loaded by at least one elastic element 29
pressing the first non return valve 6 towards a closed position.
Said at least one elastic element 29 can e.g. be a number of cup
springs 29.
[0048] In preferred embodiments of the invention, the first piston
7 has an end surface area 24 in its second end 9, which end surface
area 24 is larger than the end surface area 22 of the first end
8.
[0049] The function of the shock absorber according to the
invention will now be explained with reference to FIGS. 3 and 4 and
FIGS. 5-12. FIG. 3 shows the shock absorber 1 and the movable tool
2 at the time point t.sub.0, in a starting position before an
operating stroke. The second piston 17 rests directly on the
movable tool 2, and the movable tool 2 is at a distance Lo from a
lower part of the housing 3. As is clear from FIG. 4, the lower end
of the first piston 7 is at a distance D from the upper end of the
second piston 17. The pressure in the first chamber 4 is preferably
high, suitably a pressure in the magnitude of 10-30 MPa (100-300
bar). In one embodiment contemplated by the inventor, the pressure
in the first chamber can be 20 MPa or about 20 MPa. In the second
chamber 5 there is preferably a lower pressure than in the first
chamber 4. The pressure in the second chamber 5 is suitably 0.1-10
MPa, and preferably 1-5 MPa. Accordingly, the non return valve 6 is
kept closed, and no hydraulic liquid can move from the second
chamber 5 to the first chamber 4. Furthermore, a number of strong
cup springs 29 are acting on the first non return valve 6, in order
to additionally prevent the non return valve 6 from opening. It is
realised that the non return valve 6 also prevents hydraulic liquid
(suitably hydraulic oil) from getting from the first chamber 4 to
the second chamber 5. Also the fourth chamber 20 is filled with
pressurized hydraulic liquid, in practice usually hydraulic oil.
The fourth chamber 20 is suitably connected to the same pressure
source as the second chamber 5, and accordingly it has a pressure
in the magnitude of 1-5 MPa. By connecting the fourth chamber to
the same source of pressurized hydraulic liquid as the second
chamber, the advantage is obtained that the number of pressure
sources can be minimized. A constant oil leakage through the
throttling 33, to tank, makes sure that the liquid in the fourth
chamber 20 will not get hot or that air or particles accumulate in
the fourth chamber 20. FIG. 5 shows the situation at the time point
t.sub.1, immediately after the movable tool 2 has received a blow
from below and has started to move upwards towards the shock
absorber 1. As a consequence of the blow, the second piston 17 has
moved upwards and has met the lower end surface area 22 of the
first piston 7. Then, the second piston has to move against a
certain resistance, since the fourth chamber 20 is pressurized. A
certain amount of hydraulic liquid/oil will then be pressed out
from the fourth chamber 20, via its outlet 27. The oil that is
pressed out can be led to an accumulator 28, or via a throttling to
an oil tank 32. The resistance met by the second piston 17 is
however very small and the piston can move fairly unhindered.
Accordingly, the movable tool 2 is not much affected in its
movement. FIG. 5 shows the distance as L.sub.1, between the movable
tool 2 and the lower part of the housing 3. It is realised that the
distance L.sub.1 in FIG. 5 is somewhat less than the distance
L.sub.0 in FIG. 3. It should be understood that in practice, the
second piston 17 can move very fast, up to about 15 meters per
second. This fast pressing-in will lead to a compression of the oil
before it has time to be pressed out from the fourth chamber 20,
which in turn means that the pressure rises. Accordingly, the
outlet 27 must have a large enough cross-sectional area in order to
be able to receive the oil flow that results when the second piston
is pressed inwards in the fourth chamber. If this is not the case,
the pressure will rise fast and will become too high, which may
result in a too large premature braking of the movement of the tool
2.
[0050] FIG. 6 shows the situation at a somewhat later time point
t.sub.2 of the shock absorbing process. The second piston 17 has
begun to force the first piston 7 to move upwards through the
second chamber 5. As a result, the pressure will rise in the second
chamber 5. The pressure in the second chamber 5 is however not high
enough for the first non return valve 6 to open. Also the movable
tool 2 continues its movement and the distance is now L.sub.2
between the movable tool 2 and the lower part of the housing 3. The
distance L.sub.2 is less than the distance L.sub.1 in FIG. 5. Since
the first piston 7 has started to move upwards, the upper part of
the piston 7 will no longer bear against the lower limiting surface
area 15 for the third chamber. By the third chamber being filled
with gas (suitably air) at atmospheric pressure, instead of being
filled with hydraulic liquid, the risk of cavitation is
avoided.
[0051] FIG. 7 shows the situation at a time point t.sub.3 after
situation in FIG. 6, i.e. t.sub.3 is a later point in time than
t.sub.2. At the time point shown in FIG. 7, the second piston 7 has
moved even further into the second chamber 5. The distance between
the movable tool 2 and the lower part of the housing 3 has become
smaller and is shown as L.sub.3, where L.sub.3 is less than the
distance L.sub.2 in FIG. 6. In practice, this means that hydraulic
oil in the second chamber 5 has been exposed to a compression in
the magnitude of 1-3%. This results in a considerable increase of
the pressure in the second chamber 5, whereby the pressure
increases from a starting level of 1-5 MPa to a level that exceeds
the pressure in the first chamber 4. In practice, this can mean
that the pressure in the second chamber 5 rises all the way up to
50 MPa. Then, the cup springs 29 and the pressure in the first
chamber 4 can no longer keep the first non return valve 6 in a
closed position, but the first non return valve 6 opens and
hydraulic liquid starts to flow from the second chamber 5 to the
first chamber 4. As is most clear from FIG. 13, the first non
return valve 6 may comprise a disc shaped circular body having a
large central opening and a plurality of channels 34, through which
channels 34 hydraulic liquid can flow out. Hydraulic liquid can
also flow out into the first chamber 4 underneath the disc shaped
body that is indicated by arrows in FIG. 7. When hydraulic liquid
at high pressure is forced into the first chamber 4, the pressure
in the first chamber 4 will increase. Then, hydraulic liquid will
start to be forced out from the first chamber 4, via the outlet 10.
In principle, the outlet 10 can be closed by a valve that is
arranged quite simply to let hydraulic liquid out when the pressure
exceeds a certain predetermined level. Such a valve may be a non
return valve. According to a preferred embodiment of the invention,
the outlet 10 is connected to an accumulator 26. The accumulator 26
is preferably a bladder accumulator, such as a bladder accumulator
obtainable from HYDAC GmbH. The accumulator 26 will receive
hydraulic liquid at a high pressure, from the first chamber 4, and
will thereby store energy to be used e.g. to drive the movable tool
2. In practice, this "recovery" means that the capacity of the
pressure source need not be as large as would otherwise be
necessary.
[0052] FIG. 8 shows the situation at an even later time point, the
time point t.sub.4 that is later than t.sub.3. The movement of the
movable tool 2 has now been stopped, and the hydraulic liquid in
the second chamber 5 will not be additionally compressed. The
pressure will then start to decrease. The first non return valve 6
starts to close, under influence from the cup springs 29. FIG. 9
shows the situation at a time point t.sub.5 immediately after the
first non return valve 6 has closed (t.sub.5 is later than
t.sub.4). Now, the pressure in the first chamber 4 has decreased to
the same level as before the first non return valve 6 was opened.
In the second chamber 5, there is however a high pressure that is
above the initial pressure level in the second chamber 5. The
pressure in the second chamber 5 acts on the upper end surface area
24 of the first piston. The first piston 7 bears against the second
piston 17, which in turn bears against the movable tool 2.
Accordingly, the pressure in the second chamber 5 will act to
return the movable tool 2 back to its starting position.
[0053] FIG. 10 shows the situation at an even later time point, the
time point t.sub.6 that is later than the time point t.sub.5. As is
clear from FIG. 10, the two pistons 7, 17 have been pressed back
and thereby also the movable tool 2. The distance between the
movable tool 2 and the lower part of the housing 3 has increased to
L.sub.2. As a consequence of the first piston 7 partly being pushed
out from the second chamber 5, the pressure will decrease in the
second chamber 5. Finally, the pressure will decrease to the
original pressure level in the second chamber 5. The original
pressure level will however be maintained by opening of the second
non return valve 11, if the pressure in the second chamber 5 would
ever fall below the original pressure level. The second chamber 5
is connected, via the second non return valve 11, to a source of
pressurized hydraulic liquid, suitably hydraulic oil. Hence, the
pressure in the second chamber 5 will continue to force the pistons
7, 17 and the movable tool 2 to return.
[0054] FIG. 11 shows the situation at an even later time point, the
time point t.sub.7 that is later than the time point t.sub.6. The
movement of the first piston 7 has now been stopped, by it having
met the limiting surface area 30. The second piston 17 and the
movable tool 2 will however continue to move, partly due to
inertia. Hence, the second piston 17 will lose contact with the
first piston 7. The pressurized hydraulic liquid in the fourth
chamber 20 may then act on the upper limiting surface area 23 of
the second piston, whereby it presses the piston 17 and the tool 2
downwards. The piston 7 will not be pressed upwards, since the
upper surface area 24 of the piston 7 is larger than the lower
surface area 22 of the piston 7, while the pressure is the same in
the chambers 5, 20. It is realised of course that the relation
between the surface areas 22, 24 is not decisive as such to the
relation between the upwards acting and the downwards acting force.
What is decisive is the product of pressure and surface area. If
the pressure e.g. was higher in the second chamber 5 than in the
fourth chamber 20, the surface areas 22, 24 could be equal and the
function would still be the same. In conjunction with this, the
volume in the fourth chamber 20 increases somewhat and hence the
pressure would decrease if no new pressurized hydraulic liquid was
supplied. Oil is added primarily from the accumulator 26, and only
the oil that flows out via the throttling 33 needs to be replaced
via the non return valve 25. By the third non return valve 25, the
fourth chamber 20 is connected with a source 12 of pressurized
hydraulic liquid, suitably the same source of pressurized hydraulic
liquid that is connected to the second chamber 5. FIG. 11 shows how
the third non return valve 25 is open at the time point t.sub.8
that is later than t.sub.7, The second non return valve 11 is
however closed. Finally, FIG. 12 shows how the shock absorber has
returned completely to its starting position t.sub.9, which is
later than the time point t.sub.8. Also the third non return valve
25 is closed now (it should be understood however that the closing
of the third non return valve 25 in this case normally is not
complete, since the constant flow from the throttling 33 must be
able to get in). The tool 2 can now make its next operating stroke.
It should be understood that the above mentioned course of events
is very fast, whereby in practice the operating stroke, the shock
absorbing and the return of the tool may take as little as 2-10
milliseconds. Depending on the size of the machine, among other
things, the time for the operating stroke, the shock absorbing and
the return may however be larger. In some realistic cases, the
total time of the operating stroke, the shock absorbing and the
return may be between 100 and 500 milliseconds.
[0055] During the entire time that the first piston 7 is forced
inwards in the second chamber 5, the force that acts on its upper
end surface area 24 will slow down the movement of the movable
tool. The force is the pressure times the area of the first
piston's 7 upper end surface area 24.
F=A*P (1)
The consumed energy is the force times the distance that the tool
moves (F in Newton and S in meters):
W=F*S (2)
Or:
[0056] W=A*P*S (3)
[0057] Furthermore, W=P*V, where P=pressure and V=displaced
volume.
[0058] For a varying P:
W = V * .intg. 0 T P ( t ) t ( 4 ) ##EQU00001##
[0059] Before the non return valve 6 has risen, the pressure P in
the second chamber 5 may be considerably higher than the pressure
HP in the first chamber 4, but it will decrease to HP when the non
return valve 6 has risen. At equilibrium, the over-pressure inside
and the flow out from the second chamber 5 are in harmony with the
lifting height of the non return valve 6, and the system balances
itself at a relatively constant pressure in the second chamber
5.
[0060] Embodiments are also conceivable in which the second chamber
5 is not connected to a source 12 of pressurized hydraulic liquid.
In preferred embodiments of the invention, the second chamber 5 is
however connected to a source of pressurized hydraulic liquid.
Thereby, the advantage is attained that it is easier to return the
system to its original position, after an operating stroke.
[0061] Referring to FIGS. 14 and 15, another embodiment of the
invention will now be described. FIGS. 14 and 15 show that the
first piston 7 has an axial channel 107, in which a needle 103 is
arranged. The needle 103 is stationary arranged, preferably
stationary arranged in relation to the housing 3. The needle 103
has a conical surface area 104 in one of its ends. At least one
channel 102 is arranged inside the housing 3, and extends inwards
to the first piston 7, to mouth in an annular chamber 105 inside
the housing 3, which annular chamber 105 surrounds the first piston
7. One or more radial channels 106 inside the first piston 7
connect the annular chamber 105 with the axial channel 107 in the
first piston 7. The embodiment shown in FIGS. 14 and 15 aims at
giving the possibility to vary the distance D, i.e. the distance
that the second piston 17 must move before it gets in contact with
the first piston 7 and the true braking begins. FIGS. 14 and 15
show a stationary condition, or a starting position corresponding
to the position in FIG. 3. The outer pressure P.sub.2 is controlled
by the pressure adjusting valve 101. The outer pressure P.sub.2
will result in a flow of hydraulic liquid, such as oil, that
reaches the annular chamber 105 via the channel 102 in the housing
3. From the chamber 105, the hydraulic liquid flows via the radial
channel(s) 106 to a throttling 110 formed from the axial channel
107 and the needle 103 with its conical surface area 104. The
pressure will fall from the higher level P.sub.2 to the lower level
P.sub.3 when the hydraulic liquid passes through the throttling 110
via the channel 107, and out into the fourth chamber 20. From
there, hydraulic liquid can continue to flow through the throttling
33, to a tank T. In order for the first piston 7 to be stationary,
the pressure P.sub.3 must be balanced by the pressure P.sub.1 above
the piston, such that:
P.sub.1A.sub.1=P.sub.3A.sub.2.
[0062] Where P.sub.1=the pressure in the second chamber 5,
A.sub.1=the area of the upper surface area 24 on the piston,
P.sub.3=the pressure in the fourth chamber 20, and A.sub.2=the area
22 of the lower surface area 22 on the piston 7.
[0063] Then, there is equilibrium of forces for the first piston 7.
If the piston 7 now moves "upwards" (upwards as seen in the
drawings) from external influence, the open area of the variable
throttling 110 will decrease and the flow through the throttling
110 will decrease. Thereby, the flow through the constant
throttling 33 will decrease, whereby the pressure P.sub.3
decreases. In turn, this will result in a downwards directed net
force on the piston. Accordingly, the piston 7 will tend to be
maintained in position. A force that is applied "upwards" will
result in an increased force "downwards".
[0064] A variation of the distance D takes place in the following
way. By increasing the pressure P.sub.2, more hydraulic liquid will
flow past the variable throttling 110, which in turn leads to an
increase of the flow through the throttling 33. Then, the pressure
P.sub.3 will increase, which makes the first piston 7 move upwards
in FIG. 15, such that the distance D increases. When the piston 7
moves upwards, the open area of the variable throttling 110 will
decrease and the flow through the throttling 110 will decrease. The
flow through the throttling 110 will decrease until the pressures
P.sub.3 and P.sub.1 are once again balancing each other.
Thereafter, the same flow as before can be assumed to pass through
the variable throttling 110, but at a larger pressure drop over the
throttling 110, since its open area has decreased because P.sub.3
is formed from the flow through the throttling 33 and
A.sub.1P.sub.1=A.sub.2P.sub.3, just as before.
[0065] In all the embodiments described above, it can be assumed
that the braking force is essentially constant once the first non
return valve 6 has been opened.
[0066] Yet another embodiment will now be described with reference
to FIGS. 16 and 17. In the embodiment according to FIGS. 16 and 17,
variants are conceivable in which equal pressure and or essentially
equal pressure exists in the two chambers 4 and 20. Embodiments are
also conceivable in which there is a higher pressure in the first
chamber 4 and a lower pressure in the lower chamber 20. FIG. 16
shows schematically that the first or upper chamber 4 has a
separate source 52 of pressurized hydraulic liquid; while the lower
chamber 20 (corresponding to the fourth chamber 20 in FIG. 3) has a
separate source 12 of hydraulic liquid. The source 52 of hydraulic
liquid can be arranged to supply hydraulic liquid at a high
pressure, such as 10-30 MPa, while the source 12 of pressurized
hydraulic liquid can be arranged to supply hydraulic liquid at a
lower pressure, such as 1-5 MPa. It should be realised however that
in the embodiment in FIG. 16, the sources 12 and 52 of hydraulic
liquid can be arranged to supply hydraulic liquid at equal
pressure. It is also conceivable that the source 52 of hydraulic
liquid is eliminated and the source 12 of hydraulic liquid is
connected to both chambers 4, 20. In the embodiment shown in FIGS.
16 and 17, the first chamber 4 has been divided into an upper part
4b and a lower part 4a (it should be understood in this connection
that "upper" and "lower", respectively, and "upwards" and
"downwards" respectively, refers to that which is shown in the
drawings to be "upper" and "lower" parts, respectively. The "upper"
part 4b could also be referred to as a "distal" part and the
"lower" part as a "proximal" part, in relation to e.g. the ram tool
2 or in relation to the end of the piston 7 or one or some of the
other chambers). In FIGS. 16 and 17, the upper chamber part 4b is
narrowing in the upwards direction by being limited by a wall 38
that narrows in the upwards direction, such as a conical wall 38.
The function of this embodiment is not based on such a non return
valve 6 with an associated spring element 29 that is shown in the
embodiments according to FIGS. 1-15. Instead, the first piston 7 is
arranged to extend into the first chamber 4. In this embodiment,
the first piston 7 is provided with a collar 39. The collar 39 has
an upper surface area 41 that faces the upper chamber part or the
subchamber 4b, and a lower surface area 42 that faces the lower
chamber part 4a. The lower surface area 42 is smaller than the
upper surface area 41. As in the previous embodiments, the first
piston 7 is preferably cylindrical and also its collar 39 is
preferably cylindrical. FIGS. 16 and 17 show that the cylindrical
wall 45 of the collar 39 extends from the lower chamber part 4a and
into the upper chamber part 4b. Then, a narrow gap forms between
the wall 45 of the collar 39 and the conical wall 38. Preferably,
one or more channels 46 pass through the collar 39. In preferred
embodiments, there is a one-way valve 40 in the channel(s) 46,
which one-way valve 40 is arranged to allow for a flow through the
channel(s) 46, from the lower chamber part 4a to the upper chamber
part 4b, but to counteract or prevent a flow through the channel(s)
46 in a direction from the upper chamber part 4b to the lower
chamber part 4a. The part 7a of the piston 7 that in FIGS. 16 and
17 is positioned below the collar 39 is arranged to slide in an
opening 47 in the housing 3, having a certain length and thereby
being able to act as a guide for the first piston 7. The part 7b of
the piston 7 that in FIGS. 16 and 17 is positioned above the collar
39 is narrower than the part of the piston 7 that is positioned
below the collar 7. For example, it may have a diameter D4 that is
less than the diameter D2 of the part of the piston 7 that is
positioned below the collar 39. The upper and narrower part 7b of
the piston 7 is arranged to slide in an opening 48 in the housing
3, which opening 48 is of a certain length and acts as an upper
guide for the piston 7. FIG. 17 shows The embodiment according to
FIGS. 16 and 17 works according to the following. A blow from the
tool 2 will reach the first piston 7, optionally via a second
piston 17. The first piston 17 will then move inwards in the
chamber 4. The upper and narrower part 7b of the piston 7 will
start to leave the first chamber 4 at the same time as the piston
part 7a with a larger diameter D2 will start to penetrate into the
chamber 4. This requires that hydraulic liquid is pushed away, and
hence the piston's 7 movement will meet a resistance that results
in shock absorbing. At the same time, the collar 39 will penetrate
into the upper chamber part 4b, which leads to hydraulic liquid
being pressed from the upper chamber part 4b to the lower chamber
part 4a, via the gap between the collar 39 and the conical wall 38.
Since the wall 38 is narrowing, the gap between the collar 39 and
the wall 38 will however start to decrease as the collar 39
penetrates further into the upper chamber part 4b. Thereby, the
resistance and the shock absorbing will increase progressively.
When all the energy from the blow has been absorbed, the first
piston 7 will be in an upper (or distal) position. The pressure is
equal on both sides of the collar 39, but the upper surface area 41
on the collar 39 is larger than the lower surface area 42, since
the diameter D2 of the lower piston part is larger than the
diameter D4 of the upper piston part. Hence, the force on the upper
surface area 41 will exceed the force that acts in the opposite
direction on the lower surface area 42. Hence, the piston 7 will be
pressed back in the direction towards its starting position. During
the return movement, the hydraulic liquid will also be able to flow
through the channel or channels 46 in the collar 39, since the
one-way valve (or one-way valves) 40 will allow for this. Hydraulic
liquid can however not flow through the channel or channels 46 when
the collar 39 moves upwards in FIG. 17 (in the upper chamber part
4b). By hydraulic liquid (preferably oil) being able to flow not
only through the gap between the collar 39 and the conical wall 38,
but also through the channel or channels 46, the return movement is
facilitated such that it can be faster.
[0067] In this embodiment (if the pressure is equal in chambers 4
and 20), there can, as shown in FIG. 16, be a conduit from the
first chamber 4 to the chamber 20 that in this embodiment
corresponds to the fourth chamber 20 in the embodiment according to
FIGS. 3-13. FIG. 16 shows that a non return valve or a one-way
valve 44 is situated in the conduit 43. In case very high
pressures, "pressure peaks", temporarily would arise in the first
chamber 4, there is a risk that such pressure peaks in some cases
could have negative effects on various parts of the system. In such
cases, the conduit 43 allows for the chamber 4 to a certain extent
being relieved by the chamber 20. The non return valve 44 will
however prevent hydraulic liquid (such as oil) from flowing from
chamber 20 to the first chamber 4. If the conduit 43 interconnects
chambers 4 and 20, hydraulic liquid from the first chamber 4 can
also be received by the accumulator 28 that is connected to the
outlet for the chamber 20. It should be realised however that the
first chamber 4 could be connected, via the outlet 10, to an
accumulator 26 of its own, in the same way as is shown in e.g. FIG.
5. Such an accumulator 26 could then operate and be employed in
exactly the same way as the accumulator 26 in the embodiment
according to FIGS. 3-13. FIG. 16 however shows a variant in which
the outlet 10 of the first chamber 4 via a throttling 49 leads to a
tank 32 for accumulation of hydraulic liquid. If the non return
valve(s) 43 were missing, the pressing in of the second piston 17
in the chamber 20 could give rise to an increase in pressure in the
first chamber 4, which could effect the first piston 7 in a
direction downwards, which should be avoided.
[0068] In the embodiment according to FIGS. 16 and 17, the
downwards movement by the piston 7 could be limited by a spacing
ring 30 e.g. It should be realised that in the embodiment shown in
FIG. 16, the chamber 13 is suitably a chamber filled with gas (such
as air), which gas is preferably of atmospheric pressure or at
least has a lower pressure than the pressure in the first chamber
4.
[0069] The invention described in the present patent application is
a passive shock absorber. It is hydraulic and self-adjusting. It is
able to absorb essentially all energy from the blow in order to
store it as potential energy to be used in other parts of the
machine, primarily for the acceleration of the ram.
[0070] By the invention, the advantage is attained that the
movement of the movable tool can be slowed down in a manner that
absorbs essentially all the energy from the blow. Moreover, the
invention provides the possibility of efficient return of the tool.
By using two pistons that are initially separated from each other,
the advantage is attained that the movement of the tool is
initially slowed down very little. By using accumulators, the
advantage is among other things attained that energy recovered from
the blow could be used for a new blow.
[0071] It should be realised that the invention can be defined also
in terms of a method of shock absorbing a blow onto a movable tool,
whereby the method consists of the steps following naturally from
the use of the shock absorber according to the invention,
independent of if such steps have been explicitly mentioned or
not.
[0072] It should also be understood that the invention can be
defined in terms of a structure comprising a movable tool and a
shock absorber.
[0073] It should be realised that the various principles for shock
absorbing shown in the embodiments, can be used independent of if
the shock absorber is arranged to return the piston(s) or not.
Accordingly, the principle of progressive shock absorbing shown in
FIGS. 16 and 17 could be used also if the two surface areas 41, 42
of the collar 39 were equal. A separate device could then be
arranged for the return movement. By such an arrangement, it would
be possible efficiently to absorb the energy of the blow even if
the problem relating to the return movement would not be
solved.
[0074] It should be realised that the idea of using two pistons 7,
17 that are initially separated from each other, could be used
independent of how the shock absorber is otherwise designed.
[0075] It should also be realised that the concept of using a
pressure accumulator to handle the energy from a blow in order then
to be able to use the movable tool--or some other tool--can be used
also for other types of shock absorbers than the ones shown in the
above described embodiments.
* * * * *